Along an assembly line, various types of disposable absorbent articles, such as diapers and sanitary napkins, may be assembled by adding components to and otherwise modifying advancing, continuous webs of material. Webs of material and component parts used to manufacture diapers may include: backsheets, topsheets, absorbent cores, front and/or back ears, fastener components, and various types of elastic webs and components such as leg elastics, barrier leg cuff elastics, and waist elastics. Webs of material and component parts used to manufacture sanitary napkins may include: backsheets, topsheets, secondary topsheets, absorbent core components, release paper wrappers, and the like. In some configurations, graphics are printed on individual components and/or continuous webs of material used to assemble the absorbent articles. The graphics may be provided by printing ink on substrate materials by various printing methods, such as flexographic printing, rotogravure printing, screen-printing, inkjet printing, and the like.
In some configurations, printing operations are performed separate to the assembly process, such as for example, printing the substrates offline wherein the printed substrates may be stored until needed for production. For example, printing operations may be accomplished on discrete printing lines, separately from converting lines that are dedicated to manufacturing disposable absorbent articles. After printing on the printing lines, the printed substrates are delivered to the converting lines, such as in a form of continuous webs comprising printed images thereon. In addition to or alternatively to offline printing, graphic printing may be done online during the article assembly process.
Some current printing operations may utilize solvent and/or aqueous based inks to print graphics. However, solvent and/or aqueous based inks may require additional processing steps after the ink is printed. Such additional process steps may include drying operations that may require evaporation of some ingredient of the inks, such as a solvent or a thinner. External heating systems may also be required to complete these drying steps. As such, the required drying steps may be difficult to complete at relatively high manufacturing and/or printing speeds to ensure printed inks are adequately dried before subjecting printed substrates to additional processing operations. During the drying process, a light source such as infrared light may be used to impart energy to the ink to evaporate a solvent. And the energy imparted to the ink from the light source is proportional to the intensity of the light directed at the ink and the time during which ink is subjected to the light. The amount of energy required to dry an ink will vary based on a number of different factors. For example, for an ink deposited in a particular area of a substrate, the amount of energy required to dry the ink deposited in that area will increase or decrease along with the amount of ink deposited in that area. Thus, the intensity of the light and/or the time at which the ink is subjected to the intensity may be increased or decreased depending on the amount of ink in a particular area.
Some of the light used to dry the ink may also be absorbed by the substrate and converted into heat energy. As such, drying ink printed on heat sensitive substrates, such as nonwovens and films, may present various challenges. For example, in some configurations where printing is performed online during an article assembly process, a printed substrate may be required to advance past the light source at a relatively high rate of speed. As such, the time during which printed ink is exposed to light may be relatively short. As discussed above, in order to dry the ink in a relatively short period of time, the intensity of the light may need to be increased to relatively high levels. However, if the intensity of the light is too high over a period of time, the heat energy created in the substrate by the light may destroy and/or damage the advancing substrate. In some instances, a light source may be configured to heat an advancing substrate web to a temperature that is below a softening point of the substrate material. However, even though the light source may not heat the substrate enough to damage the substrate, enough heat may be imparted to the substrate to change the modulus of elasticity of the substrate. In turn, the change in the modulus of elasticity of the substrate may result in a phase shift during the printing operation, wherein some ink is applied to the substrate in undesired locations. Such phase shifts may be readily noticeable in printed regions, and in turn, may detract from aesthetically pleasing aspects of the printed regions.
Consequently, there remains a need to configure ink printing systems to help ensure that ink printed on a substrate can be dried at relatively high speeds without damaging the substrate and/or causing undesired phase shifts in printing operations caused by changes in the modulus of elasticity of the substrate.